How else would two people know if they're sexually compatible?
One wouldn't buy a vehicle without taking it out for a drive, nor would one buy a pair of shoes without trying them on. So why would one marry someone without knowing they would be sexually compatible? You wouldn't. Of course the Dubs only think of the actual physical mechanics of sex, and the mechanics are pretty much common universally.
Personally, now that I do not have THAT goofy conduct ban hanging over my head I have found that "recreational" sex is some of the BEST sex. I am an official member of the 4-F club.